U.S. patent number 4,578,431 [Application Number 06/528,197] was granted by the patent office on 1986-03-25 for process for improving melt strength of ethylene polymers by treatment with organic peroxide.
This patent grant is currently assigned to Mobil Oil Corporation. Invention is credited to Peter J. Canterino, Richard G. Shaw.
United States Patent |
4,578,431 |
Shaw , et al. |
March 25, 1986 |
Process for improving melt strength of ethylene polymers by
treatment with organic peroxide
Abstract
Melt strength of polyethylene and ethylene-higher olefin
copolymers during processing is improved by pretreating the polymer
in melt form at a temperature of at least 230.degree. C. in the
presence of an organic peroxide for a period of time equal to at
least three times the half-life of the organic peroxide at the melt
temperature.
Inventors: |
Shaw; Richard G. (Bradley
Beach, NJ), Canterino; Peter J. (Towaco, NJ) |
Assignee: |
Mobil Oil Corporation (New
York, NY)
|
Family
ID: |
24104644 |
Appl.
No.: |
06/528,197 |
Filed: |
August 31, 1983 |
Current U.S.
Class: |
525/387;
525/333.8 |
Current CPC
Class: |
C08F
8/00 (20130101); C08J 5/18 (20130101); C08K
5/14 (20130101); C08F 8/00 (20130101); C08F
110/02 (20130101); C08F 8/00 (20130101); C08F
210/16 (20130101); C08K 5/14 (20130101); C08L
23/06 (20130101); C08K 5/14 (20130101); C08L
23/0815 (20130101); C08J 2323/26 (20130101); C08F
2810/10 (20130101); C08J 2323/30 (20130101) |
Current International
Class: |
C08F
8/50 (20060101); C08F 8/00 (20060101); C08F
008/08 () |
Field of
Search: |
;525/333.8,387 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Lipman; Bernard
Attorney, Agent or Firm: McKillop; Alexander J. Gilman;
Michael G. Trojnar; Edward J.
Claims
What is claimed is:
1. A process treating a film-forming copolymer of ethylene and an
olefin having 4 to 8 carbons atoms, or of a high density ethylene
homopolymer, comprising:
heating said ethylene copolymer in melt form at a temperature of
from about 230.degree. C. to 340.degree. C. in the presence of an
effective amount of from 100 ppm to 2000 ppm of an organic peroxide
for a period of time equal to at least three times the half-life of
the organic peroxide at the heating temperature to increase the
melt strength of said copolymer so that the copolymer is suitable
for extrusion into a film by blown film extrusion.
2. The process of claim 1 in which said ethylene polymer is a
copolymer of ethylene and an olefin having 4 to 8 carbon atoms and
a density of 0.90 to 0.94.
3. The process of claim 1 in which said ethylene polymer is high
density ethylene homopolymer.
4. The process of claim 1 in which said ethylene polymer is
ethylene-hexane copolymer.
5. The process of claim 1 in which said ethylene polymer is treated
for a period of time equal to at least five times the half-life of
said organic peroxide at the pretreating temperature.
6. The process of claim 1 in which the pretreating temperature is
between about 230.degree. C. and 280.degree. C.
7. The process of claim 1 in which said peroxide is a
di(tertiary-substituted) peroxide.
8. The process of claim 1 in which said peroxide is dicumyl
peroxide.
9. The process of claim 1 in which said peroxide is
di(tertiary-butyl) peroxide.
Description
BACKGROUND OF THE INVENTION
Film made from ethylene-higher olefin copolymers, known as linear
low density polyethylene, has toughness properties superior to film
made from conventional low density polyethylene prepared under high
pressure conditions. However, linear low density polyethylene has a
low melt strength so that it is difficult to process at high speed
and maintain a stable bubble in the blown tubular film process. The
disadvantage of lower melt strength is also apparent in the blow
molding of linear low density polyethylene and high density
polyethylene. In accordance with this invention melt strength of
polyethylenes can be improved without substantially affecting their
desirable properties.
SUMMARY OF THE INVENTION
The melt strength of polyethylene and ethylene-higher olefin
copolymers during processing is improved by pretreating the
polyethylene polymer or copolymer in melt form, in the presence of
an organic peroxide for a period of time equal to at least three
times the half-life of the peroxide at the melt temperature.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with this invention the melt strength of ethylene
polymers during processing by formation into films or by blow
molding is improved by pretreating the ethylene polymer in melt
form in the presence of an organic peroxide for a period of time
equal to at least three times the half-life of the peroxide at the
polymer melt temperature. Preferably, the time is selected so that
the organic peroxide is substantially decomposed during the
pretreatment step. Therefore, it is preferred that the period of
time of pretreatment be equal to at least five times of the
half-life of the organic peroxide at the pretreating
temperature.
The processing temperature can vary widely within a lower limit
which is the practical melt temperature of the polymer and a higher
temperature under which degradation of the polymer occurs. Thus,
temperatures in the range of 120.degree. C.-340.degree. C.
preferably from 230.degree. C. to 280.degree. C. can be used.
Temperatures of about 260.degree. C. have been found to be suitable
with dicumyl peroxide.
The nature of the organic peroxide is not critical to this
invention. The essential requirement is that the peroxide chosen
have a half-life which permits its substantial decomposition at
effective melt temperatures in a reasonable residence time. Thus,
di (tertiary substituted) peroxides have been found suitable.
Examples include dicumyl peroxide and di(t-butyl) peroxide.
Generally, the amount of peroxide can vary from about 100 ppm to
2000 ppm based on the weight of the ethylene polymer. Preferably
the amount of peroxide is 100 ppm to 1000 ppm.
The peroxide can be incorporated in any convenient manner. It has
been found advantageous to spray the peroxide as a solution in a
volatile solvent such as acetone onto the powdered polymer.
Following removal of the solvent the polymer can be heated to a
moderate temperature of about 60.degree. C. and sealed containers
for several hours to allow the peroxide to diffuse into the
polymer. Then the polymer containing peroxide can be subjected to
the melt treatment in any suitable apparatus such as an
extruder.
The invention is illustrated by the following non-limiting
example.
EXAMPLE 1
Linear LDPE, (ethylene-butene copolymer), available from Union
Carbide as GRSN 7040 (2 MI, 0.920 density) was mixed with different
amounts of dicumyl peroxide and extruded at 260.degree. C.
(500.degree. F.). The resin was treated by spraying with an acetone
solution of the peroxide evaporating the acetone, tubling in a drum
blender and heating in an oven at 60.degree. C. in a sealed
polyethylene bag to allow the peroxide to diffuse into the resin.
The melt strength of the resulting products were measured with a
melt tensiometer and compared with a 2 MI, 0.920 density branched
LDPE.
______________________________________ Melt RPM to PPM Strength
Break Melt Peroxide (grams) (rpm)
______________________________________ Linear Extruded Resin 0 0.86
3000 " 100 1.95 2200 " 500 2.96 471 " 750 4.05 548 Branched LDPE
LMA-000 0 3.93 518 LWA-000 0 3.18 637
______________________________________
It can be seen that the melt strength was increased to the same
level as is obtained with the branched polyethylene.
EXAMPLE 2
In a manner similar to Example 1 a series of ethylene-butene
copolymers were treated and extruded at 260.degree. C. through a 1
inch Sterling unit. The melt index (MI) of the extruded samples is
listed in the Table.
TABLE ______________________________________ MI
______________________________________ Control (stabilized resin)
1.9 RESIN +0 ppm peroxide 1.1 " +100 ppm peroxide 0.67 " +500 ppm
peroxide 0.11 " +750 ppm peroxide 0.08
______________________________________
On the blown film line the resin cured with 100 ppm peroxide
processed into 1 mil film with improved bubbled stability as
compared with the control. The 30 mm line was used to make 1 mil
film at 2/1 BUR and 30 fpm. The head pressure increased from 1600
to 1900. The other two resins (500 and 750 ppm peroxide) could not
be drawn down to 1 mil. The melt was too elastic and broke whenever
a gel came through, instead of flowing around it as occurred in the
control and 100 ppm peroxide modification.
Although the present invention has been described with preferred
embodiments, it is to be understood that modifications and
variations may be made without departing from the spirit and scope
of the invention as those skilled in the art will readily
understand.
* * * * *